I plugged the oil breather on my ‘70 F100 302...

[Sisujoel]

... and now I’ve got oil blow-by spray on the passenger side of the engine compartment. The drivers side is clean and dry. I realize (after reading forum posts thinking I may have a leaking valve cover gasket) that I made a boneheaded mistake by plugging the breather cap. The breather cap is original and I learned that it would’ve originally had a hose routed from it to the air filter cover. When I acquired the truck it had no breather hose and a mismatched air filter cover so I installed an aftermarket open flow style air filter holder.

Questions: what possible damage might I have done by plugging the breather cap? Fortunately I only drove the truck a couple times for short distances before noticing the oil spray. What would be the most likely source of the passenger side oil leak/blow back? Valve cover gasket? Since I don’t have an original air filter cover to route the breather cap to should I replace the original cap with a mesh filter style breather cap?

Live and learn.

[Jacksdad]

I guess there's always a chance you could damage a seal or unseat a gasket, but you probably didn't do anything other than make a mess.

[Busboy]

There would be no permanent damage but it sounds like the engine is toast with that amount of blowby.

[tnlprt]

The original breather cap had the hose routed to the air cleaner for only one purpose.
To filter the air being sucked into the crankcase

A mesh or K and N style breather will work just fine.

Likely no damage occurred.

Blow by is a product of ring seal ..Live with it or rebuild it

The most you have done is blown the valve cover gasket or the end seals on the intake . Hope for the valve cover gasket.

[Sisujoel]

I appreciate the replies. Lesson learned.